Internal combustion engine fuel injector having an electromagnetic metering valve

ABSTRACT

The injector has a hollow body housing the body of the metering valve, which has a discharge hole for discharging the usual control chamber. The hole comes out at a flat surface of the valve body, and is engaged by a flat surface of a plate, under the control of an armature of an electromagnet. The armature is in the form of a disk, has substantially no stem, is connected to the hollow body by a leaf spring hinge, and has a surface having a spherical-bowl-shaped recess. A ball is located between the recess and another recess carried by a second surface of the plate. The valve body is fixed to the hollow body by a ring nut of a given height. And, to cover the distance between the valve body and the armature, a spacer member is preferably formed in one piece with the valve body.

[0001] The present invention relates to improvements to an internalcombustion engine fuel injector having an electromagnetic meteringvalve.

BACKGROUND OF THE INVENTION

[0002] Known injectors of the above type comprise a hollow body forhousing the metering valve body; the valve body has a calibrated holefor discharging high-pressure fuel from an injection control chamber;the calibrated hole is kept closed by a normally disk-type shuttercontrolled by the armature of a control electromagnet, and normallycomes out at a conical depression in a surface of the valve body; theshutter comprises a ball cooperating with a plate engaged by thearmature and having a spherical-bowl-shaped recess to eliminate anymisalignment between the hole axis and displacement of the armature; andthe valve body is locked inside a cavity in the hollow body by a ringnut, which requires a given distance between the electromagnet and thevalve body.

[0003] Known injectors of this type have several drawbacks. Inparticular, the distance between the valve body and the electromagnetmeans the disk-type armature must be provided with a corresponding stemto act on the plate; the armature stem, in turn, calls for high-costguide means, normally precision-machined sleeves; machining the valvebody with the conical depression is also relatively expensive; and,finally, the conical depression increases the necessary length of thearmature stem.

[0004] In one known injector, a valve body is proposed in which thecalibrated hole comes out at a flat surface of the valve body, and isclosed by a flat surface of a plate, another surface of which may alsobe flat and is engaged by a convex end of the armature stem. In analternative solution, the other surface of the plate has aspherical-bowl-shaped recess engaged by a complementary appendix on thestem. This known injector does not eliminate the need for an armaturestem, and, what is more, makes the armature stem even more expensive.

[0005] Another injector has recently been proposed, in which the valvebody is defined by a sleeve force-fitted inside a cavity in the hollowbody; and the disk-type armature is connected to the hollow body by aleaf spring hinge having one portion fixed to the hollow body, and oneportion fixed to the armature. This reduces the distance between thevalve body and the electromagnet, but, on account of the conical surfaceof the valve body at which the calibrated hole comes out, the disk-typearmature, to act on the plate, calls for a spacer member normallycarried by the armature.

[0006] This type of injector is also relatively expensive, on account ofthe spacer member and relative connection. Moreover, on account of theleaf spring hinge, the armature movement is not perfectly straight, sothat the contact surfaces between the spacer member on the armature andthe shutter plate are subject to relative transverse slippage, whichreduces the sensitivity and reliability of the valve, and whichincreases alongside an increase in the distance of the point at whichthe spacer member engages the plate.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide improvementsto a fuel injector, such as to achieve a high degree of reliability andlow cost, and to eliminate the aforementioned drawbacks of knowninjectors.

[0008] According to the present invention, there is provided an internalcombustion engine fuel injector having an electromagnetic meteringvalve, and comprising a hollow body in which is housed a valve bodyhaving a calibrated discharge hole for discharging high-pressure fuelfrom a control chamber of the injector; said discharge hole coming outat a flat surface of said valve body; and said metering valve comprisinga plate having a flat first surface for closing said discharge holeunder the control of an armature of an electromagnet; characterized inthat said armature is connected to said hollow body by a leaf springhinge having a first portion fixed to said hollow body, and a secondportion fixed to said armature; a ball being located between saidarmature and a second surface of said plate.

[0009] According to a further aspect of the invention, the valve body ishoused inside a cavity of said hollow body, and is locked by a threadedring nut; a spacer member being defined by an appendix projecting fromsaid valve body towards said armature, so as to minimize the transversemovement, caused by said leaf spring hinge, of said plate with respectto said discharge hole.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A number of preferred, non-limiting embodiments of the inventionwill be described by way of example with reference to the accompanyingdrawings, in which:

[0011]FIG. 1 shows a partial longitudinal section of an internalcombustion engine fuel injector in accordance with a first embodiment ofthe invention;

[0012]FIG. 2 shows a partial longitudinal section of a fuel injector inaccordance with a further embodiment of the invention;

[0013]FIG. 3 shows a section along line III-III in FIGS. 1 and 2;

[0014]FIG. 4 shows a larger-scale detail of FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Number 5 in FIG. 1 indicates as a whole an internal combustionengine fuel injector having an electromagnetic metering valve 6.Injector 5 comprises a hollow body 8 having a central cavity 9 housing abody 11 of metering valve 6—hereinafter referred to as “valve body”.

[0016] More specifically, valve body 11 is defined by a sleeve 12, andby a plug member 13 having an integral cylindrical appendix 15 housed insleeve 12. Plug member 13 has a calibrated hole 14 for discharging fuelfrom metering valve 6; and sleeve 12 is force-fitted inside cavity 9, soas to rest on a shoulder 16 of cavity 9, and comprises an annular groove17 in which is formed a calibrated inlet hole 18 by which pressurizedfuel is fed into metering valve 6.

[0017] Plug member 13 comprises a disk-shaped portion 19 which forms aflat shoulder 20 with appendix 15; shoulder 20 rests, in use, on a topedge 21 of sleeve 12, so as to compress a seal 22; plug member 13 islocked against sleeve 12 by a threaded ring nut 23 screwed inside hollowbody 8; and the ring nut acts on an annular portion 30 of the topsurface of disk-shaped portion 19.

[0018] Calibrated hole 14 of plug member 13 is normally kept closed by ashutter—indicated as a whole by 24—which is kept in the closed positionby an armature 25 of an electromagnet 26. Armature 25 is normally pusheddownwards by a compression spring 27; annular groove 17 is located atthe outlet of a feed conduit 28 communicating with a fitting 29 forfeeding pressurized fuel to injector 5; and, via a substantiallylongitudinal conduit 35, conduit 28 also supplies a fuel atomizer nozzlecarried by hollow body 8 and not shown in the drawings.

[0019] A nozzle control rod 31 slides inside sleeve 12, and comprises atop surface 32 which is normally kept a given distance from the bottomsurface of appendix 15 of plug member 13 by the pressurized fuelentering a control chamber 33 of injector 5 through calibrated hole 18.Control chamber 33 is substantially defined by the gap between topsurface 32 of rod 31 and the bottom surface of appendix 15 of plugmember 13.

[0020] Armature 25 is substantially defined by a disk having a flat topsurface 34 cooperating with a pole face 36 of the usual magnetic core 37of electromagnet 26, and has radial slits 38 through which the fueldischarged flows, through calibrated hole 14, to a drain conduit (notshown) of injector 5.

[0021] Armature 25 is connected to hollow body 8 by a leaf spring hingeindicated as a whole by 39. For which purpose, core 37 of electromagnet26 is locked in known manner against a shoulder 41 of hollow body 8 withthe interposition of a spacer ring 42 made of rigid metal. Leaf springhinge 39 (see also FIG. 2) comprises an annular portion 43 fixed tohollow body 8, in particular, gripped between core 37 and ring 42.

[0022] Leaf spring hinge 39 also comprises a portion defined by anelastic radial tongue 44 having one end integral with annular portion43. The other end of tongue 44 is fixed to a central portion of armature25, e.g. is gripped between armature 25 and a washer 45 in turn fixed toarmature 25, so that the movement of armature 25 substantially comprisesrotation about the point of connection of tongue 44 to annular portion43.

[0023] Spacer ring 42 is of the minimum height enabling armature 25 tobe housed and to move between shoulder 41 and annular portion 43 of leafspring hinge 39; whereas, since ring nut 23 must be of considerableheight for reasons of strength, the disk of armature 25 is located agiven distance from the top surface of disk-shaped portion 19 of plugmember 13.

[0024] To activate injector 5, electromagnet 26 is energized temporarilyto attract armature 25 in opposition to the force of spring 27. Armature25 rotates by a very small angle about the point of connection of tongue44 to the annular portion of leaf spring hinge 39; the pressurized fuelin control chamber 33 therefore opens shutter 24, thus reducing the fuelpressure, so that rod 31 moves upwards to open the fuel atomizer nozzle.

[0025] When electromagnet 26 is deenergized, spring 27 restores armature25 to the FIG. 1 position by rotating it by a very small angle in theopposite direction to the opening direction, thus closing shutter 24;the fuel pressure in control chamber 33 is therefore restored, so thatrod 31 moves back down into the nozzle-closing position shown in FIG. 1.

[0026] To reduce the machining cost of plug member 13, discharge hole 14comes out at a central portion 46 of the top surface of disk-shapedportion 19. The surface of portion 46 must be machined to a high degreeof precision so as to be perfectly flat and perpendicular to the axis ofdischarge hole 14.

[0027] Shutter 24 of discharge hole 14 comprises a plate 48 having aflat first surface 49 (see also FIG. 4) for engaging the surface ofportion 46; and a ball 50 located between armature 25 and a secondsurface 51, opposite surface 49, of plate 48. And surface 51 has aspherical-bowl-shaped recess 52 for engaging ball 50.

[0028] Armature 25 in turn comprises a central portion 53 having abottom surface 54 opposite top surface 34 of armature 25; and surface 54also has a spherical-bowl-shaped recess 56 for engaging ball 50.

[0029] On account of the distance between the disk of armature 25 andthe top surface 30, 46 of disk-shaped portion 19 in the FIG. 1embodiment, central portion 53 of armature 25, to reduce the thicknessof plate 48, may be carried by a spacer member defined by a cylindricalappendix 57 projecting towards plate 48; and the top surface of centralportion 46 of disk-shaped portion 19 may in turn be coplanar with thesurface of annular portion 30.

[0030] A shallow annular groove 58 between the surfaces of portions 30and 46 ensures more effective closure of hole 14 by plate 48; and thespherical bowls of recesses 52 and 56 may advantageously be slightlylarger in diameter than ball 50 to center ball 50 more easily.

[0031] The top surfaces of portions 30 and 46 of disk-shaped portion 19may therefore be machined simultaneously, thus reducing the cost of plugmember 13.

[0032] In the FIG. 2 embodiment, in which the same parts as in FIG. 1are indicated using the same reference numbers with no furtherdescription, plug member 13 of valve body 11 is defined by a disk 59having an annular top surface 61 engaged by ring nut 23, and a flatbottom surface 62. For inlet hole 18 to communicate with control chamber33, a top portion 63 of rod 31 has a small diameter, and the gap betweenportion 63 and sleeve 12 increases the volume of control chamber 33.

[0033] Armature 25 has no downward-facing cylindrical appendix, and itscentral portion 53 is substantially flush with, or projects slightlywith respect to, the bottom edge of the disk of armature 25. The centralportion 46 of disk 59, on the other hand, is carried by a spacer memberdefined by a cylindrical appendix 64 facing disk 59 and of such a heightas to enable use of a shutter 24 of limited thickness, e.g. the one inFIG. 1.

[0034] In the FIG. 2 embodiment also, surface 49 of plate 48 engages thesurface of central portion 46 of disk 59 of valve body 11, and ball 50is located between central portion 53 of armature 25 and the secondsurface 51 of plate 48.

[0035] As such, both plug member 13 and the disk of armature 25 in FIG.2 are relatively cheap to produce; the movable assembly of armature 25in FIG. 2 is lighter than in FIG. 1, thus increasing the response speedof metering valve 6; and recess 56 in portion 53 of armature 25 in FIG.2 is closer to the fulcrum of leaf spring hinge 39 than in FIG. 1, thusreducing the transverse movement of recess 56, and therefore of ball 50and plate 48, with respect to discharge hole 14.

[0036] Clearly, further changes and improvements can be made to theinjector as described herein without, however, departing from the scopeof the accompanying claims. For example, the gap between armature 25 andplug member 13 may be covered by placing both central portions 46 and 53of plug member 13 and armature 25 on appendixes of substantially thesame height; injector 5 in FIG. 1 may be provided with a valve body 11with plug member 59 in FIG. 2, and the FIG. 2 injector may be providedwith a valve body 11 with plug member 15, 19 in FIG. 1; and, in bothcases, valve body 11 may be formed in one piece.

1) An internal combustion engine fuel injector having an electromagneticmetering valve, and comprising a hollow body (8) in which is housed avalve body (11) having a calibrated discharge hole (14) for discharginghigh-pressure fuel from a control chamber (33) of the injector; saiddischarge hole (14) coming out at a flat surface of said valve body(11); and said metering valve (6) comprising a plate (48) having a flatfirst surface (49) for closing said discharge hole (14) under thecontrol of an armature (25) of an electromagnet (26); characterized inthat said armature (25) is connected to said hollow body (8) by a leafspring hinge (39) having a first portion (43) fixed to said hollow body(8), and a second portion (44) fixed to said armature (25); a ball (50)being located between said armature (25) and a second surface (51) ofsaid plate (48). 2) An injector as claimed in claim 1, characterized inthat said second surface (51) is opposite said first surface (49), andhas a spherical-bowl-shaped recess (52) for engaging said ball (50). 3)An injector as claimed in claim 1, characterized in that said armature(25) is in the form of a disk having a flat first surface (34) facingsaid electromagnet (26) and connected to said second portion (44) of theleaf spring hinge (39); said armature (25) also comprising a secondsurface (54) facing said plate (48) and having a spherical-bowl-shapedrecess (56) for engaging said ball (50). 4) An injector as claimed inclaim 2, wherein said valve body (11) is housed inside a cavity (9) ofsaid hollow body (8), and is locked by a threaded ring nut (23);characterized in that at least one of said surfaces (51, 54) havingspherical-bowl-shaped recesses (52, 56) is carried by a correspondingspacer member (57, 64). 5) An injector as claimed in claim 4,characterized in that said spacer member is defined by an appendix (57)projecting from said valve body (11) towards said armature (25), so asto minimize the transverse movement, caused by said leaf spring hinge(39), of said ball (50) with respect to said discharge hole (14). 6) Aninjector as claimed in claim 4, characterized in that said spacer memberis defined by an appendix (57) projecting from said armature (25)towards said valve body (11); said flat surface of said valve body (11)being carried by a central portion (46) which is coplanar with a surfaceof an annular portion (30) engaged by said ring nut (23). 7) An injectoras claimed in claim 5, characterized in that said valve body (11)comprises a sleeve (12) force-fitted inside said cavity (9); and a plugmember (13) comprising a disk-shaped portion (19, 59) which is locked tosaid sleeve (12) by said ring nut (23).